HOX Gene Expression in Drosophila melanogaster
Introduction Hox, or homeotic genes, are a group of genes that control the body plan development of an embryo. They code for the development of the embryo along the anterior-posterior axis. In fruit flies the hox proteins determine the type of segment structures, while in humans they influence the different types of vertebral segments. They give the segments an identity, while it takes many other proteins to actually form the segments. Hox genes are of interest because of their amount of conservation across evolutonarty lines despite morphological differences, and the fact then when absent or mutated, major deformities or death usually occur. Discovery of the Homeobox The homeobox is a sequence about 180 base pairs long which enocde for the regulatory nuclear proteins. These homeoproteins act as transcription factors that are able to bind to DNA. The collection of these proteins called the homeodomain, are believed to regulare the formation of body structures by regulating the expression of targeted genes. This group of proteins were discovered by a group of scientists in 1984. Mutants that survived and were observable had body parts in the wrong location, such as a leg where the antenna should be located. W. McGinnis et al. # First clones containing an H repeat sequence protein known to be important in the formation of fly anatomy were isolated. They were then put through a hybridization process to make sure they coded for the repeat. # Then 30,000 bacteriophages were screened for the H repeat probes, and the 24 best signaling probes were purified. # Then recombinant DNA was digested and the clones DNA was ran through a gel to determine the appearance of the H repeat. # Of the 19 that showed the repeat, 2 locations were found coded for in the genome, and called p93 and p99. # The location of these proteins on the chromosomes were found by marking them and looking for hybridization. # Spatial restriction of p93 during embryo development was determined by discetingg the CNS of the flies. # Spatial restriction of p99 was determined by examining a blastoderm and were found in about 60% to 65% of the embryo's length from the posterior end. # Cell ablation experiments in both of these regions showed p93's importance in the development of the most posterior 5 or 6 neuromeres. Also these showed p99's importance in first thorasic and posterior head development. Further Research Much more research has since been done on the types of genes that control the different regions of development, and the amount of similarity between the genes in different organisms. Work has also been done to examine the effect of mutations in these gene regions. References "Hox Gene." Wikipedia. Wikimedia Foundation, 24 Oct. 2014. Web. 27 Oct. 2014. "Homeobox." Wikipedia. Wikimedia Foundation, 24 Oct. 2014. Web. 27 Oct. 2014. McGinnis, W., M. S. Levine, E. Hafen, A. Kuroiwa, and W. J. Gehring. "A Conserved DNA Sequence in Homoeotic Genes of the Dosophila Antennapedia and Bithorax Complexes." Nature 308 (1984). Nature Publishing Group. Web. Jones, Bradley, and William McGinnis. "A New Drosophila Homeobox Gene, Bsh, Is Expressed in a Subset of Brain Cells during Embryogenesis." Development 117 (1993): 793-806. The Company of Biologists Limited. Web.